1. Field of the Invention
The present invention relates to an apparatus and method for ink jet printing, and, more particularly, to an apparatus and method in which printing is performed by ink discharged from a discharge port and attached onto a printing medium such as a textile.
2. Related Background Art
An ink jet head applicable to an ink jet printing apparatus generally has a discharge port for discharging ink, a liquid channel for supplying ink to the discharge port, an energy acting portion in the liquid channel and energy generating means for generating energy which acts on ink in the energy acting portion to discharge ink from the discharge port.
Exemplary energy generating means are an electromechanical converter such as a piezoelectric element or the like, electromagnetic wave energy generating means for applying an electromagnetic wave such as a laser or the like to the ink to form flying liquid droplets, or an electrothermal converter, all which have been well-known.
An ink jet printing head provided with heat energy generating means generally uses electrothermal converters as the heat energy generating means, and has electrodes, liquid passage walls and a top plate provided on a substrate through processes like those used for manufacturing semiconductors, which processes incorporate various techniques including etching, vapor deposition, sputtering or the like. Since the ink discharge ports used for forming the flying liquid droplets required for printing can be readily arranged with high density, such an ink jet printing head has the following advantages.
a) The ink jet printing head can be easily fabricated and it can perform high resolution printing. PA1 b) A compact constitution of the ink jet printing head can be provided. PA1 c) In the process of manufacturing the recording head, the advantages of IC (integrated circuit) technology or miniaturization technology, which have been recently significantly improved from the viewpoint of reliability and progress in the field of semiconductor manufacturing, can be adopted as much as possible. It is also possible to provide a recording head with a two-dimensional array of discharge ports. PA1 an ink jet printing apparatus including at least one printing head having a plurality of discharge orifices for discharging ink toward a textile printing medium in response to drive signals corresponding to an image to be printed on the printing medium, a scanning mechanism for moving the printing head relative to the printing medium and beyond edges thereof in a width direction, a sub-scanning mechanism for conveying the printing medium in a sub-scanning direction transverse to the direction of movement of the printing head, control circuitry for setting a print beginning position and a print ending position for the scanning mechanism, wherein the print beginning position is spaced a predetermined distance from one edge of the printing medium in the width direction and the print ending position is spaced a predetermined distance from another edge of the printing medium in the width direction, and drive signal supply circuitry for supplying drive signals to the printing head to discharge ink therefrom while the printing head is moved by the scanning mechanism, wherein the drive signal supply circuitry supplies drive signals to the printing head to discharge ink therefrom from the print beginning position to the print ending position; PA1 means for drying the printing medium after recording the image thereon; PA1 means for fixing the colors in the printing medium; and PA1 means for cleaning the printing medium having the color fixed therein.
With the above-described points considered, a multinozzle recording head with high nozzle density can be attained without difficulty, and a large quantity of recording heads can be manufactured with high productivity and at low production cost.
It is known to provide such a printing head, using an electrothermal converter as the heat energy generating means and manufactured through processes of manufacturing semiconductors and having multi-nozzles, with a liquid passage corresponding to each ink discharge port, an electro-thermal converter in each liquid passage, and a common liquid chamber from which ink is supplied to the liquid passages.
FIG. 15 shows an example of a conventional ink jet printing head 1401 provided with such heat energy generating means. This printing head has electrothermal converters as heat energy generating means 1403, electrodes 1404, liquid passage walls 1405 and a top plate 1406 provided on a substrate 1402, manufactured using processes for manufacturing semiconductors that use various techniques including etching, vapor deposition, sputtering or the like.
Printing liquid (ink) 1412 is supplied from a printing-liquid tank (not shown) to the common liquid chamber 1408 of the printing head 1401 through a liquid supply pipe 1407 connected to the chamber 1408 by a connector 1409. The printing liquid 1412 supplied to the common liquid chamber 1408 is supplied to liquid passages 1410 in accordance with capillary phenomena and forms a meniscus in each liquid discharge port or nozzle 1411 at the corresponding end of each liquid passage 1410 to stably retain the liquid at the corresponding port 1411.
To discharge the printing liquid by utilizing the printing head constructed above, for instance, the electrothermal converters 1403 are energized. As a result, printing liquid located on and in the vicinity of the electrothermal converters 1403 is rapidly heated. The rapid heating thereof produces film boiling in the printing liquid 1412, which forces liquid droplets to be discharged from the liquid discharge ports 1411. Such an ink jet printing head can be obtained with ease and high productivity, with an arrangement of liquid discharge ports at a high density such as 16 ports/mm, for example and with multiple (128 to 256) nozzles.
Among the ink jet printing apparatus using such a head, a serial type printing apparatus adopts a serial scan method of scanning the head in a main-scan direction crosswise to the sub-scan printing medium conveying direction. The printing head is mounted on a carriage movable in a main-scan direction along the printing medium, and the printing medium is fed in the sub-scan direction by a predetermined amount corresponding to the length of the array of liquid discharge ports on the printing head, whereby the next line of the image can then be printed on the printing medium. The head scanning and printing medium conveying are thus repeated until the entire printing medium has been printed.
In order to prevent non-discharge or misdischarge of ink from the printing head during a printing operation and to recover the discharge capabilities of the printing head, a recovery operation is properly performed on the printing head before the start of a printing operation. This is necessary in part because the printing operation is performed by repeatedly discharging ink from the ink jet printing head shown in FIG. 15, which also produces numerous minute satellite ink mist droplets. This ink mist attaches and accumulates on a discharge face of the printing head 1401. When the amount of the ink mist is large, it can clog the ink discharge ports and prevent ink discharge. In addition, faulty ink discharge can be caused by adhesion of foreign matter on the discharge face or invasion of foreign matter or air into the liquid channels.
In order to solve these problems, a recovery operation is performed; for example, ink is forcibly circulated between the ink jet head and the ink tank to remove the cause of ink non-discharge or misdischarge.
In such a serial type printing method, the printing head can be mounted on a compact printer, which has the advantage of easy handling and installation. The same printing head can also be mounted on a large-size printer that can print on a printing medium having a long width in the scanning direction of the printing head, and therefore printers for various applications can use the same printing head.
FIG. 16 is a perspective view showing one type of conventional printing apparatus using the ink jet printing head shown in FIG. 15.
The ink jet printing apparatus is largely constituted of a frame 1506, two guide rails 1507 and 1508, an ink jet head 1509 and a carriage 1510 for the movement thereof, an ink supply device 1511 and a carriage 1512 for the movement thereof, a head recovery device 1513, and an electronic system 1505.
The ink jet head 1509 (hereinafter sometimes referred to simply as a head) comprises a plurality of columns of discharge ports which respectively discharge ink of magenta (M), cyan (C), yellow (Y) and black (BK), and converters for converting an electric signal into energy for use in discharging the ink, and is further provided with means for generating the electric signals for selectively discharging the ink through the columns of discharge ports in accordance with an image signal sent from an image processing unit. The head may be a print head which discharges the ink by the use of heat energy, as discussed above in connection with FIG. 15.
As discussed above, the apparatus forms an image 1517 (indicated by shading in FIG. 16) on the printing medium 1536 by repeatedly scanning the head 1509 in the main scanning direction H. After each scan, the recording medium is advanced in the sub-scanning direction B and the head 1509 is scanned across the printing medium again. This is repeated until the entire image is recorded. FIG. 16 illustrates unrecorded bands at the edges of the printing medium produced with conventional apparatus.
The ink supply device 1511 serves to store ink and supply a necessary amount to the head, and comprises an ink tank and an ink pump (both not shown) or other components. This device 1511 and the head 1509 are connected via an ink supply tube 1515, whereby the head 1509 is automatically supplied with the ink, owing to its capillary action, in an amount corresponding to that discharged. In a head recovery operation that will be later described, ink is compulsorily supplied to the head 1509 by using the ink pump.
The head 1509 and the ink supply device 1511 are mounted on the head carriage 1510 and the ink carriage 1512, respectively, for reciprocal movement along the guide rails 1507, 1508 by a driving device, not shown.
The head recovery device 1513 is provided at a home position (waiting position) of the head and opposed to the head. It maintains the stability of ink discharge from the head 1509, and is movable forward and a backward in the direction of the arrow A to perform the following specific operations.
First, the head recovery device 1513 provides a cap for the head 1509 at the home position (capping operation) to retard the evaporation of ink from the nozzles of the head 1509. Further, it serves in the operation of compulsory discharge of ink through the nozzles by pressurizing the ink flow channels within the head 1509 using an ink pump (a pressure recovery operation) to force bubbles or dirt out of the nozzles into the cap before the start of image recording, or performs an operation of sucking ink through the nozzles (a suction recovery operation).
The head recovery device also can clean the discharge surface of the head 1509 by wiping the discharge surface to prevent an unstable discharge condition, when ink mist, generated incidentally with the discharge of ink during a printing operation, attaches on or adjacent to the discharge port.
An ink receiver 1540 is located between a platen 1532 and the head recovery device 1513 for receiving preliminarily ejected ink. The ink receiver comprises plural caps and is positioned corresponding to the height of each head. When the printing duty of a particular image is low, some ink discharge ports may not be used during a printing operation, so that the viscosity of the ink in such ports may increase due to evaporation of the ink solvent. To prevent this condition from affecting ink discharge, the ink jet head is driven by predetermined drive pulses, and the ink is discharged from all discharge ports, prior to a printing operation. This operation is called "purging."
The above-mentioned preliminary discharge (purging) is also performed to prevent color mixture that can be caused by the head recovery device which wipes the discharge face of the ink jet head. When wiping the discharge face, the wiping is performed using a blade of rubber-like material. In this operation, the different colors of ink are sometimes forced into other discharge ports and cause a color mixture in those ports. However, the mixed-color ink will be discharged to the ink receiver as a result of such preliminary discharge, and therefore improper color mixture on the printing medium can be prevented.
The ink jet printing apparatus constructed as just described can print a fine image at high speeds, and noise produced during the printing operation is low because the printing is done without impacting the printing medium. In addition, since the printer uses multi-colored inks and can easily print a color image, the ink jet printer can be used with a computer and wordprocessor or the like, or as printing means in a stand-alone printing machine such as a copying machine, a printer, a facsimile machine or the like.
On the other hand, in recent years, in addition to the usual print mediums, such as plastic sheets for an overhead projector, or processed paper with punched holes or paper with perforations, free-sized paper and woven cloth are desired to be used as the print medium. As to the size of the print medium, for example, a sheet to be used for an advertisement or woven cloth to be used for clothes, large-size print mediums are sometimes necessary.
It has been proposed that such an ink jet printing apparatus be used for textile printing by discharging the ink directly onto the cloth (see, for example, Japanese Patent Publication No. 63-31594). In such ink jet printing, as distinguished from the case of printing characters on a printing medium, the edge portion of the print medium must be printed. Therefore, the print head must be in good ink discharge condition as soon as it begins to print from the edge portion of the print medium. Accordingly, to accomplish high quality printing, it is necessary to complete the discharge recovery operation and the preliminary discharge operation before beginning printing on the print medium.
According to the aforementioned conventional ink jet printing apparatuses, as stated above, it is necessary to perform separate discharge recovery and preliminary discharge operations before the printing operation begins. Because the ink receiver must be provided in the printing apparatus, it is difficult to make the printing apparatus compact. In addition, the high viscosity ink collected in such operations can be difficult to handle. In addition, the printing operation must be interrupted for preliminary discharge of ink to the ink receiver, and therefore the time to complete a printing operation is increased.